Silicone gel compositions are prepared as addition reaction-curable organopolysiloxane compositions comprising an organohydrogenpolysiloxane having a silicon-bonded hydrogen atom (i.e., SiH group), an organopolysiloxane having a silicon-bonded alkenyl group such as vinyl, and a platinum-based catalyst wherein addition reaction of the silicon-bonded hydrogen atom to the alkenyl group yields cured products. The silicone gel compositions are heat cured into silicone gel cured products (i.e., cured silicone gels), which find use in the protection of electronic parts including automobile electronic parts and consumer electronic parts because of improved heat resistance, weather resistance, oil resistance, freeze resistance, and electrical insulation as well as low elastic modulus and low stress. The low elastic modulus and low stress which are characteristic of the cured silicone gel are not available from other elastomer products. The recent demand for automobile and consumer electronic parts having higher reliability imposes an increasing need to impart heat resistance to a silicone gel material for encapsulation.
In typical silicone rubbers, loading of fillers such as carbon and iron oxide is an effective means for improving heat resistance. However, the filler loading is not readily acceptable as the means for improving the heat resistance of silicone gel materials, which are required to have low viscosity and transparency, because there emerge such disadvantages as transparency lowering, filler settlement, and poor workability due to increased viscosity.
JP-A 2008-291148 (Patent Document 1) describes the use of a cerium metal salt as the means for imparting heat resistance. However, cerium which is a rare earth element is problematic in steady availability. A new means for imparting heat resistance is thus desired.
Recently, JP-A 2015-007203 (Patent Document 2) describes the use of iron carboxylate as the means for imparting heat resistance. In either of JP-A 2008-291148 and JP-A 2015-007203, the metal salt must be mixed with an organopolysiloxane and heat treated to form a reaction product prior to addition. Therefore, problems of process shortening and simple material supply remain unsolved.